1. Field of the Invention
The present invention relates to a silicon carbide semiconductor device, and in particular to a silicon carbide semiconductor device having a junction gate.
2. Description of the Background Art
As a power semiconductor device, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and an IGBT (Insulated Gate Bipolar Transistor) have been widely used (see, for example, B. J. Baliga et al., “The insulated gate rectifier (IGR): A new power switching device,” IEDM Tech. Dig., 1982, pp. 264 to 267). An IGBT has a configuration combining a MOSFET and a bipolar transistor, and thereby has a high-speed operation as in a MOSFET and a low ON resistance and a high breakdown voltage as in a bipolar device.
As a material for power semiconductor devices, silicon (Si) has been conventionally widely used. It is expected that performance such as ON resistance will be significantly improved by using silicon carbide (SiC) having a larger band gap instead of Si.
Thus, it is expected that a power semiconductor device having a lower ON resistance and a higher breakdown voltage than before can be obtained by using an IGBT instead of a MOSFET, and using SiC instead of Si as a material. However, an IGBT using SiC has not been industrially put into practical use, partly because, when SiC is used, channel mobility in a MOS structure included in the IGBT is significantly lower than a theoretical value, which results in a higher ON resistance. Therefore, a method for improving channel mobility in a MOS structure using SiC has been under consideration (see, for example, Japanese Patent Laying-Open No. 2011-023675).
However, even with the method described in the above publication, it is considered difficult to obtain channel mobility sufficiently close to a theoretical value. Thus, it is considered still impossible to obtain a low ON resistance and a high breakdown voltage which are theoretically expected when SiC is used instead of Si and an IGBT is used instead of a MOSFET.